Hi Haiyang, Thank you for your summary.
One important thing is that we must not skip any call to ReorderBufferXidSetCatalogChanges() (direct or indirect) during fast-forwarding or building snapshot, because the historic snapshot only tracks txns with catalog changes, the v6-0004 seems to skip it in xact_decode(). Here is a related bug: https://www.postgresql.org/message-id/flat/tencent_3A071B760AA1A38540B57F297332B7781C08%40qq.com -- Regards, ChangAo Chen
